1. Field of the Invention
The present invention relates to a quantum device wherein quantum dots are arrayed in a two-dimensional configuration. The quantum dots arrayed on the quantum device can be preferably used as a single-electron transistor, doping diode, is doping transistor, doping transistor array and semiconductor light emitting device.
2. Description of Related Art
Devices that utilize single-electron tunnel effect such as single-electron transistors and single-electron memories are attracting much attention. The single-electron transistor, for example, is a promising candidate that can replace MOSFETs to satisfy the requirements of miniaturization of devices to the order of sub-micron for which improvements on the MOSFETs, the mainstream technology in the field of semiconductor transistors, are reaching limitations thereof.
A fine particle surrounded by a thin insulation layer receives electrons from an external electrode by the tunnel effect. Because the particle has a capacitance C with respect to the outside, electrostatic energy of the particle changes by e2/2C when an electron enters therein. This prohibits a subsequent electron from entering the fine particle by the tunnel effect. Therefore, in order to fabricate the device utilizing the single-electron tunnel effect, it is inevitable to arrange quantum dots on an insulator, the quantum dots being formed from microscopic metal particles having electrostatic energy higher than energy ΔE (approximately 25 mV) required for thermal excitation of an electron at room temperature. In case e2/2C has a low value, it is inevitable to make an array of quantum dots having energy just above the Fermi level of a microscopic dot higher than the thermal excitation level of electron. Although single-electron operation is lost in this case, transistor operation can still be achieved. Also, microscopic lead wires must be formed even when a quantum device can be achieved, because the tunnel effect does not occur with wide lead wires of conventional circuits due to parasitic capacitance accompanying the lead wires.
As a single-electron memory, a prototype device was made as a fine line (100 nm wide) of polycrystal Si film having an extremely small thickness of 3.4 nm and a gate electrode (100 nm) crossing each other via an oxide film gate of 150 nm by depositing a-Si in a depressurized CVD process and crystallizing it at 750° C. (Japanese Journal of Applied Physics: Vol. 63, No. 12, pp. 1248, 1994). This device operates at room temperature and has potential for the use as an nonvolatile memory which operates at a speed exceeding the limitation of the conventional flash memory. Also, an aluminum-based, single-electron transistor having an island electrode measuring 20 nm was fabricated by means of electron beam lithography and triangular shadow evaporation technologies (Jpn. J. Appl. Phys., Vol. 35, 1996, pp. L1465–L1467). This single-electron transistor has advantages which are not found in silicon-based devices, for example, a periodical gate modulation characteristic wherein background current does not depend on the gate voltage.
However, the single-electron memory based on the polycrystal Si film is unstable because there are variations in the Si film thickness. Also, the Al-based, single-electron transistor operates at 100 K, far below the room temperature, and is not of practical use.